android java.lang.nullpointerexception

Question

我想在android中做這樣的事情。我的意思是，我有密碼的文本框，我試圖使人們看到一個文本視圖，如果密碼是正確的，但我還是不斷呈現出異常java.lang.nullpointerexception這裏是我的代碼

public class MainActivity extends Activity { 
    EditText Password; 
    Button login; 
    TextView txtDash; 



    @Override 
    public void onCreate(Bundle savedInstanceState) { 
     super.onCreate(savedInstanceState); 
     setContentView(R.layout.activity_main); 

     Password=(EditText)findViewById(R.id.pass); 
     login=(Button)findViewById(R.id.login); 

     login.setOnClickListener(new View.OnClickListener() { 
      @Override 
      public void onClick(View V) { 
       try { 
       if (Password.getText().toString().equals("dsml")) 
       { 

        txtDash.setVisibility(View.VISIBLE); 
        login.setVisibility(View.INVISIBLE); 
        Password.setVisibility(View.INVISIBLE); 

       } 
       else 
       { 
        Toast.makeText(getBaseContext(), "invalid password - try again", Toast.LENGTH_SHORT).show(); 
       } 
       }catch(Exception e){ 
        //Log.e("log_tag", "Error"+e.toString()); 
        Toast.makeText(getBaseContext(), e.toString(), Toast.LENGTH_SHORT).show(); 
       } 
      } 
     }); 


    } 

    @Override 
    public boolean onCreateOptionsMenu(Menu menu) { 
     getMenuInflater().inflate(R.menu.activity_main, menu); 
     return true; 
    } 
} 

請任何一個幫助getout這

Answer 1

它看起來像你缺少你使用它之前到txtDash參考。

txtDash = (View)findViewById(R.id.id_for_your_view); 

Answer 2

給從XML佈局文件的txtDash refrence像作爲密碼，登錄

Password=(EditText)findViewById(R.id.pass); 
login=(Button)findViewById(R.id.login); 

txtDash=(TextView)findViewById(R.id.txtdas); <<< You Forgot this line...